Hot gas bypass system for a refrigeration system utilizing a plurality of eutectic plates

ABSTRACT

A refrigeration system includes a plurality of hold-over plates of the type in which an eutectic is frozen by the use of a circulating refrigerant. The hold-over plates are in a closed refrigeration circuit with a compressor, condenser and receiver. In order to provide continuous compressor operation at the lowest safe suction pressure after the eutectic is frozen, there is a hot gas connection between the compressor output and the plate input to bypass compressor discharge gas through each plate. This increases the velocity of the refrigerant flowing through the plates, as well as insuring that the evaporating pressure of the refrigerant does not go below a predetermined minimum danger point. Instead of operating below the minimum danger point or shutting off on low-pressure cut-out, the compressor continues to operate at an acceptable suction pressure to effectively reduce the temperature of air and product within the space being refrigerated.

United States Patent- [191 Lauterbach HOT GAS BYPASS SYSTEM FOR A REFRIGERATION SYSTEM UTILIZING A PLURALITY OF EUTECTIC PLATES [75] Inventor: William E. Lauterbach, Evanston,

Ill.

[73] Assignee: Dole Refrigeration Company,

' Chicago, Ill.

22 Filed: Apr. 21, 1972 21 Appl. No.: 246,158

[52] US. Cl 62/200, 62/278, 62/439 [51] Int. Cl. F25b 41/00 [58] Field of Search 62/199, 196, 200, 278, 439

[56] References Cited' Jan. 29, 1974 Primary Examiner-Meyer Perlin Attorney, Agent, or Firm-Parker, Plyer & McEachran [5 7] ABSTRACT A refrigeration system includes a plurality of holdover plates of the type in which an eutectic is frozen by the use of a circulating refrigerant. The hold-over plates are in a closed refrigeration circuit with a compressor, condenser and receiver. In order to provide continuous compressor operation at the lowest safe suction pressure after the eutectic is frozen, there is a hot gas connection between the compressor output and the plate input to bypass compressor discharge gas through each plate. This increases the velocity of the refrigerant flowing through the plates, as well as insuring that the evaporating pressure of the refrigerant does not go below a predetermined minimum'danger point. Instead of operating below the minimum danger point or shutting off on low-pressure cut-out, the compressor continues to operate at an acceptable suction pressure to effectively reduce the temperature bran and product within the space being refrigerated;

1 Claim, 1 Drawing Figure HOT GAS BYPASS SYSTEM FOR A REFRIGERATION SYSTEM UTILIZING A PLURALITY OF EUTECTIC PLATES SUMMARY OF THE INVENTION The present invention relates to a refrigeration system utilizing a hot-gas bypass capacity control arrangement to provide improved refrigeration performance and compressor protection after the eutectic in the hold-over plates is frozen.

One purpose of the invention is a refrigeration system of the type described utilizing a hot gas bypass between the compressor output and the plate inputs.

Another purpose is a hot gas bypass of the type described utilizing a distributor to insure that all of the plates receive an adequate amount of gas.

Another purpose is a refrigeration system of the type described utilizing a distributor to convey hot gas to all of the plates, and a check valve between the output of the distributor and the input of each plate to prevent refrigerant passing from one plate to another during the refrigeration cycle when hot-gas is not being bypassed.

Another purpose is a refrigeration system of the type described which permits continuous running of the compressor at a low suction pressure without losing oil to the plates.

Another purpose is a refrigeration system of the type described which provides lower temperatures within the space being cooled than heretofore possible with hold-over plates.

Another purpose is a refrigeration system of the type described which prevents undesirable low-pressure cycling of the compressor after the eutectic is frozen, minimizing electrical problems and avoiding possible liquid refrigerant migration.

Another purpose is a refrigeration system of the type described which prevents a servicing mechanic from jeopardizing the compressor by mindlessly setting the low-pressure cut-out switch below the safe limit.

Other purposes will appear in the ensuing specification, drawing and claims.

BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in the attached diagrammatic showing of a refrigeration system.

DESCRIPTION OF THE PREFERRED EMBODIMENT Hold-over refrigeration plates are indicated at l0, l2 and I4 and they may typically be of the type shown in U. S. Pat. No. 2,859,945. Each plate consists ofa steel pan and cover which are welded together to form an air tight container, at serpentine steel tube coil for the primary refrigerant, and steel channels and tube spacers which serve to hold the coil in position and to maintain the thickness dimension. The container is filled, under vacuum, with an eutectic which is a precise mixture of an inorganic salt and water that freezes and melts at a given constant temperature. To this mixture may be added an inhibitor to prevent electrochemical anaerobic corrosion, a freezing starter to prevent subcooling of the liquid phase, a softening agent to prevent hard freezing which might damage the plate, and other additives for special purposes. The vacuum serves to hold the assembly solidly together and to prevent internal aerobic corrosion. The channels are designed and located so as to transmit heat in a desired manner during freezing or melting of the eutectic. The exterior of the plate may be zinc metallized to provide protection against corrosion. In operation, holdover plates are mounted by suitable hangers on the ceiling and/or walls of a truck body. The eutectic is frozen at dockside by feeding refrigerant such as R-12 or R-502 to the plate coils from a closed-circuit truck-mounted condensing unit. On the route the eutectic melts, providing the refrigerating effect necessary to protect the product.

Each of the plates 10, 12 and 14 have a refrigerant output line connected in common to a heat exchanger 16. The output of the heat exchanger passes through a crankcase pressure regulating valve 18, with the valve output being connected to an accumulator 20. The output of the accumulator is connected to the compressor 22. The compressor output is connected to a condenser 24, with the output of the condenser 24 being connected to a receiver 26. The receiver output passes through a sight glass 28 and through a dryer 30 and then to a solenoid valve 32. The refrigerant line from the receiver then passes through the heat exchanger and is connected to a plurality of expansion valves indicated at 34, 36 and 38. As is conventional, the output of each of the expansion valves is connected to the input of one of the plates l0, 12 or 14. Each of the expansion valves have a remote thermal bulb, indicated at 42, in communication with the power assembly and clamped on the output line of each of the plates, which controls the refrigerant feed through the valve as is conventional. Each of the expansion valves also may have an external equalizer line, indicated at 40, which is connected from the power assembly of the expansion valve to the output of each of the plates which provides for more accurate control of the expansion valves, as is conventional.

In a typical R-502 refrigeration system of the type described, the compressor has an output of hot gas at a pressure of approximately 215 psig and a superheated temperature of approximately 250 F. After the hot gas has passed into the condenser, it will condense into a liquid at a temperature of approximately 100 F. The 100 F. liquid passes into the heat exchanger where it is effective to dry the gas coming from the hold-over plates, thus removing any liquid droplets in the gas passing to the compressor. The accumulator also functions to remove any liquid slugs in the gas directed to the compressor input. At the input side of each of the expansion valves the refrigerant is in a liquid state at a pressure of approximately 210 psig and at a temperature of approximately F. On the output side of the expansion valve the refrigerant is a mixture of gas and liquid and is at a pressure of approximately 10 psig and a temperature of 29 F. The refrigerant is passed through the eutectic within the plates to cause the eutectic to freeze. The liquid evaporates during the process and the gas passes through the heat exchanger where it is dried, as described above, and then flows to the accumulator and the compressor.

In a system of the type described, oil from the compressor is circulated with the refrigerant. At times, particularly at low suction pressure, there can be an accumulation of oil in the hold-over plates, known as oil logging, which can cause damage to the compressor as it takes the oil needed to operate the compressor away from it and deposits this oil within the plates. There is a greater tendency for oil logging in holdover plates than in finned-tube blower-coil evaporators. Various methods have been tried in the past to prevent oil logging, but none have been entirely reliable. The problem arises in hold-over plate systems due to the reduction in heat load once the eutectic is frozen. The reduction in heat load causes the temperature, pressure and velocity of the refrigerant within the plate all to drop to such a low level that oil flowing with the refrigerant may accumulate in the plates and not flow back to the compressor. Generally, there is no problem during the period that the eutectic is being frozen, as the heat load is high and hence the refrigerant within the plates is moving at an adequate velocity. However, if the lowpressure cut-out is set too low, once the eutectic is frozen and the heat load rapidly drops, the velocity of the refrigerant within the plate is not sufficient and oil may be deposited within the plates causing a loss of oil to the compressor.

This problem has been overcome, in the present invention, by providing a hot gas bypass from the output of the compressor to the input of the plates, holding the pressure of the refrigerant within the plates above a predetermined minimum, and thus insuring that the compressor will not cycle off, but will run continuously. in addition, the use of hot gas or the introduction of hot gas at the input of the plates increases the velocity of the refrigerant moving through the plates, insuring that the oil will be swept through the plates and will not remain as an accumulation or deposit. Thus, there are two advantages brought about by the introduction of hot gas from the compressor output to the input of each of the plates. The hot gas maintains the temperature pressure and velocity of the refrigerant in the plates at such levels that oil will not accumulate within the plates and tends to sweep any oil deposits out of the plates.

A hot gas bypass valve is indicated at 44 and has its input connected through a solenoid 46 to a line 48 which is connected to the compressor output. A line 50 is connected between the valve 44 and the compressor input to transmit suction pressure to the valve power assembly for the purpose of controlling the valve oper-- ation. The output from the bypass valve 44 is connected by a line 52 to a distributor 54 which may be of the type manufactured by the Sporlan Valve Company of St. Louis, M0. The distributor 54 has a number of outputs equal to the number of plates, as it is essential that each of the plates receive an adequate amount of gas to raise the pressure and temperature of the refrigerant and to increase the velocity of the refrigerant. It is not necessary that the gas distributed to each plate be equal, but there must be an adequate supply for each plate. The outputs from the distributor 54 are connected through check valves 56 to the output side of each of the expansion valves. The check valves prevent refrigerant from being fed between plates in the event there is any slight difference in refrigerant pressure in the various plates occasioned by normal modulation of the expansion valves during the refrigeration cycle when the bypass valve is not feeding hot gas.

Solenoid 46 may be used when the system is to be pumped down for maintenance. Any type of shut-off valve is satisfactory for this function.

Basically, the invention consists in providing a hot gas bypass between the compressor output and the plate inputs with the distribution system being arranged such that each of the plates gets an adequate amount of the hot gas, enough to raise the pressure and temperature of the refrigerant, and to increase the velocity of the refrigerant to sweep any oil accumulation out of the plates. By permitting the compressor to run continuously under a safe operation condition, which is accomplished by the hot gas bypass, the temperature of air and product within the space being cooled can effectively be lowered, as compared with a system in which there is no hot gas bypass. A typical plate system without a hot gas bypass may have an external plate temperature of 20 F., whereas the same system with a hot gas bypass may have an external plate temperature of 40 F. Once the eutectic is frozen, and even though the heat load is lowered, the refrigerant will continue to pass through the plates, thus continuing to lower the external plate temperature. The hot gas maintains the refrigerant above a predetermined minimum, but the refrigerant continues to be at a sufficiently low temperature to effectively supercool the external surfaces of the plates.

Whereas the preferred form of the invention has been shown and described herein, it should be realized that there may be many modifications, substitutions and alterations thereto.

I claim:

1. In a refrigeration system a plurality of holdover plates, an expansion valve at the input of each plate, a compressor, condenser and receiver, a connection between the receiver and the input of each expansion valve, and a connection between the output of each plate and the compressor,

the improvement comprising a hot gas connection between the compressor output and the input of each plate, said hot gas connection including a vapor distributor connected at its input to the compressor output, a hot gas bypass control valve connected between the compressor output and the distributor input, a plurality of outputs from said distributor, one for each plate, each distributor output being connected between the output of an expansion valve and the input of a plate and a plurality of backflow check valves, one in each connection between said distributor and a plate input. 

1. In a refrigeration system a plurality of holdover plates, an expansion valve at the input of each plate, a compressor, condenser and receiver, a connection between the receiver and the input of each expansion valve, and a connection between the output of each plate and the compressor, the improvement comprising a hot gas connection between the compressor output and the input of each plate, said hot gas connection including a vapor distributor connected at its input to the compressor output, a hot gas bypass control valve connected between the compressor output and the distributor input, a plurality of outputs from said distributor, one for each plate, each distributor output being connected between the output of an expansion valve and the input of a plate and a plurality of backflow check valves, one in each connection between said distributor and a plate input. 